class Container {
  static of(value) {
    return new Container(value)
  }

  constructor(value) {
    this._value = value
  }

  map(fn) {
    return Container.of(fn(this._value))
  }
}

class Maybe {
  static of(x) {
    return new Maybe(x)
  }

  isNothing() {
    return this._value === null || this._value === undefined
  }

  constructor(x) {
    this._value = x
  }

  map(fn) {
    return this.isNothing() ? this : Maybe.of(fn(this._value))
  }
}

//练习1：使用fp.add(x,y)和fp.map(f,x) 创建一个能让functor里的值增加1的函数ex1

const fp = require('lodash/fp')
let maybe = Maybe.of([5, 6, 1])
let ex1 = () => {
  maybe = maybe.map(value => {
    return fp.map(i => fp.add(i, 1), value)
  })
  return maybe
}
// console.log(ex1())
// console.log(ex1())

//练习2：实现一个函数ex2， 能够使用fp.first获取列表的第一个元素

let xs = Container.of(['do', 'ray', 'me', 'fa', 'so', 'la', 'ti', 'do'])
let ex2 = () => {
  return xs.map((value) => {
    return fp.first(value)
  })
}

// console.log(ex2()._value)

//练习3：实现一个函数ex3，使用safeProp和fp.first找到user的名字的首字母

let safeProp = fp.curry(function(x, o) {
  return Maybe.of(o[x])
})
let user = {id: 2, name: 'Albert'}
let ex3 = () => {
  return safeProp('name', user)._value
}
// console.log(ex3())

//练习4：使用Maybe重写ex4，不要有if语句

// let ex4 = function(n) {
//   if(n) {
//     return parseInt(n)
//   }
// }

let ex4 = (n) => {
   return !Maybe.of(n).isNothing() && parseInt(n)
}
// console.log(ex4(3.4))